diff --git a/subprojects/solver/solver-smtlib/src/main/java/hu/bme/mit/theta/solver/smtlib/solver/SmtLibItpSolver.java b/subprojects/solver/solver-smtlib/src/main/java/hu/bme/mit/theta/solver/smtlib/solver/SmtLibItpSolver.java
index 98667ad383..07bd23df1d 100644
--- a/subprojects/solver/solver-smtlib/src/main/java/hu/bme/mit/theta/solver/smtlib/solver/SmtLibItpSolver.java
+++ b/subprojects/solver/solver-smtlib/src/main/java/hu/bme/mit/theta/solver/smtlib/solver/SmtLibItpSolver.java
@@ -22,7 +22,14 @@
 import hu.bme.mit.theta.core.type.booltype.BoolType;
 import hu.bme.mit.theta.core.type.enumtype.EnumType;
 import hu.bme.mit.theta.core.utils.ExprUtils;
-import hu.bme.mit.theta.solver.*;
+import hu.bme.mit.theta.solver.Interpolant;
+import hu.bme.mit.theta.solver.ItpMarker;
+import hu.bme.mit.theta.solver.ItpMarkerTree;
+import hu.bme.mit.theta.solver.ItpPattern;
+import hu.bme.mit.theta.solver.ItpSolver;
+import hu.bme.mit.theta.solver.SolverStatus;
+import hu.bme.mit.theta.solver.Stack;
+import hu.bme.mit.theta.solver.UnknownSolverStatusException;
 import hu.bme.mit.theta.solver.impl.StackImpl;
 import hu.bme.mit.theta.solver.smtlib.dsl.gen.SMTLIBv2Lexer;
 import hu.bme.mit.theta.solver.smtlib.dsl.gen.SMTLIBv2Parser;
@@ -39,12 +46,13 @@
 import org.antlr.v4.runtime.CharStreams;
 import org.antlr.v4.runtime.CommonTokenStream;
 
-import java.util.ArrayList;
 import java.util.Collection;
-import java.util.List;
+import java.util.HashSet;
 import java.util.Set;
 
-import static com.google.common.base.Preconditions.*;
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkState;
 
 public abstract class SmtLibItpSolver<T extends SmtLibItpMarker> implements ItpSolver {
 
@@ -254,7 +262,7 @@ protected final GeneralResponse parseResponse(final String response) {
     }
 
     private void declareDatatypes(final Collection<Type> allTypes) {
-        List<Type> types = new ArrayList<>(allTypes);
+        Set<Type> types = new HashSet<>(allTypes);
         types.removeAll(typeStack.toCollection());
         for (Type t :
                 types) {